The invention relates to a household coffee machine of the type which includes a flow heater, a cold water supply, and a hot water outflow, a thermostat for controlling the temperature of the flow heater, and a heat detector-equipped switch operable to actuate a calcification indicator device.
There does exist a household coffee machine, of the type described above, in which the switch for actuating the calcification indicator is a heat actuated switch whose heat detector is arranged at the hot water outflow of the flow heater. In this device, the switch is series connected with the calcification indicator device, the latter giving a signal before the calcine deposits in the water flow path of the heater reach an inadmissible extent and impair the performance of the appliance.
This prior appliance also contains a thermostat that interrupts the heater filament circuit of the flow heater as soon as the heater exceeds a given temperature.
This known device has a drawback inasmuch as the heat detector of the switch controlling the calcification indicator device is mounted in the hot portion of the line issuing from the flow heater. With this arrangement, after termination of the water flow through a new appliance, or a not calcified appliance, or a calcified appliance, steam is generated in and flows through the water line. This steam causes a temperature rise which is detected by the heat detector. In response to this temperature rise, the heat detector opens the heater filament circuit and actuates the calcification indicator.
Further, in this known appliance, the flow heater works subsequent to the water heating process as a hot plate or pot warming element. Thus, there exists the risk that the calcification indicator device will respond also during the heat holding period (i.e., the period while the coffee pot heat is being maintained) since the holding temperature of such a flow heater lies substantially above operating temperature during the water heating process.
For the reasons noted above, no clear calcification indication is assured in the device described.
There is also a coffee machine known that consists of a cold water container, a check valve, an electric flow heater, a feedpipe and a filtering device. This other machine also includes a calcification indicator device whereby a differential pressure gage arranged between the check valve and the outlet of the flow heater is disposed in working connection with the calcification indicator device. In this case the indicator device may be an optical and/or acoustical signaler. Since even a transient or short-term pressure rise in the flow heater is indicated by means of the differential pressure gage, no clear indication of the state of calcification is thereby assured. Moreover, since a pressure rise may appear during operation of the flow heater when it is not calcified, the indicating device can be actuated when there is no calcification at all.
The present invention is intended to create a household coffee machine having a calcification indicating device that assures a reliable indication of the state of calcification. The invention accomplishes this in that the calcification indication device (including series-connected switch) is connected in parallel with the heating thermostat and that the heat detector for the calcification indicator is arranged at the cold water supply.
According to the invention, the switch condition of the heating thermostat during the water heating process, that is, during the making of the coffee, is used for the indication of calcification. That is to say, the calcification indication device is actuated when the flow heater attains, during the water heating process, such a temperature that the heating thermostat becomes actuated to a "cut-out" condition. Through the switch of the calcification indicator being actuated to an "open" condition in response to the conclusion of the coffee making period, the calcification indication device is switched off after termination of the water heating process so that heating of the flow heater after the water heating process can no longer affect the calcification indicator.
In comparison to the resistance of the heating thermostat, the calcification indication circuit (i.e. indicator and switch) is preferably designed for relatively high-impedance in order to insure that the calcification indication device does not respond when the heating thermostat switch is closed.
Upon excessive calcification of the appliance occurring, i.e. with a certan degree of lime precipitation occurring in the flow heater, the heating thermostat switch is actuated to an open condition because of the resulting temperature rise in the flow heater. The calcification indicator switch remains closed until the coffee making is concluded. The heat detector of the calcification indicator switch is affected by the temperature of the cold water in such a way that the switch remains closed until the water heating process is concluded.